DoS Attacks

Denial of Service (DoS) Attracks

A denial of service (DoS) attack is an
attack that clogs up so much memory on the target system that it can not serve
it's users, or it causes the target system to crash, reboot, or otherwise deny
services to legitimate users.There are several different kinds of dos attacks
as discussed below:-

1) Ping Of Death
:-The ping of death attack sends oversized
ICMP datagrams (encapsulated in IP packets) to the victim.The Ping command
makes use of the ICMP echo request and echo reply messages and it's commonly used
to determine whether the remote host is alive. In a ping of death attack,
however, ping causes the remote system to hang, reboot or crash. To do so the
attacker uses, the ping command in conjuction with -l argument (used to specify
the size of the packet sent) to ping the target system that exceeds the maximum
bytes allowed by TCP/IP (65,536).example:- c:/>ping -l 65540 hostname
Fortunately, nearly all operating systems these days are not vulnerable to the
ping of death attack.

2) Teardrop Attack :-Whenever data is sent
over the internet, it is broken into fragments at the source system and
reassembled at the destination system. For example you need to send 3,000 bytes
of data from one system to another. Rather than sending the entire chunk in
asingle packet, the data is broken down into smaller packets as given below:
* packet 1 will carry bytes 1-1000.
* packet 2 will carry bytes 1001-2000.
* packet 3 will carry bytes 2001-3000.
In teardrop attack, however, the data packets sent to the target computer
contais bytes that overlaps with each other.
(bytes 1-1500) (bytes
1001-2000) (bytes 1500-2500)
When the target system receives such a series of packets, it can not reassemble
the data and therefore will crash, hang, or reboot.
Old Linux systems, Windows NT/95 are vulnerable.

3) SYN - Flood Attack :- In SYN flooding attack, several SYN packets are sent to the
target host, all with an invalid source IP address. When the target system
receives these SYN packets, it tries to respond to each one with a SYN/ACK
packet but as all the source IP addresses are invalid the target system goes
into wait state for ACK message to receive from source. Eventually, due to
large number of connection requests, the target systems' memory is consumed. In
order to actually affect the target system, a large number of SYN packets with
invalid IP addresses must be sent.4) Land Attack :-A land attack is similar
to SYN attack, the only difference being that instead of including an invalid
IP address, the SYN packet include the IP address of the target sysetm itself.
As a result an infinite loop is created within the target system, which
ultimately hangs and crashes.Windows NT before Service Pack 4 are vulnerable to
this attack.

5) Smurf Attack :-There are 3 players in
the smurf attack–the attacker,the intermediary (which can also be a
victim) and the victim. In most scenarios the attacker spoofs the IP source
address as the IP of the intended victim to the intermediary network broadcast
address. Every host on the intermediary network replies, flooding the victim
and the intermediary network with network traffic.Result:
- Performance may be degraded such that the victim, the
victim and intermediary networks become congested and unusable, i.e. clogging
the network and preventing legitimate users from obtaining network services.

6)
UDP - Flood Attack :-Two
UDP services: echo (which echos back any character received) and chargen (which
generates character) were used in the past for network testing and are enabled
by default on most systems. These services can be used to launch a DOS by
connecting the chargen to echo ports on the same or another machine and
generating large amounts of network traffic.

7) Distributed
Denial Of Service (DDoS) :- In Distributed DoS attack, there are 100 or more different
attackers (systems) attacking the single system. Due to higher number of
attackers DDoS attack is more effective and dangerous than regular DoS attack.
The attackers have control over master zombies, which, in turn, have control
over slave zombies, as shown in figure.

No system connected to the internet is
safe from DDoS attacks. All platforms, including Unix
and Windows NT, are vulnerable to such attacks. Even Mac OS machines have been
used to conduct DDoS attacks.

8) Distributed
Denial Of Service with Reflectors (DRDoS) :-In
DRDoS attacks the army of the attacker consists of master zombies, slave
zombies, and reflectors. The difference in this type of attack is that slave
zombies are led by master zombies to send a stream of packets with the victim's
IP address as the source IP address to other uninfected machines (known as
reflectors), exhorting these machines to connect with the victim. Then the
reflectors send the victim a greater volume of traffic, as a reply to its
exhortation for the opening of a new connection, because they believe that the
victim was the host that asked for it. Therefore, in DRDoS attacks, the attack
is mounted by noncompromised machines, which mount the attack without being
aware of the action.

a DRDoS attack creates a greater volume of traffic
because of its more distributed nature, as shown in the figure below.